Magnetic disk drive and magnetic disk drive system

ABSTRACT

A magnetic disk drive that shape coefficient is 3.5 inches are provided, which is designed as rotating magnetic media in a high speed in order to consume a low electric power, to generate a less heat, and to access more quickly.  
     When magnetic disk media are rotated in a higher speed, an electric power consumption and a heat generation are increased because of a load increase in rotating the magnetic disk media. An avoidance of such problems and setting an additional special cooling mechanism to magnetic disk drive systems, for example, disk array systems, is presented.  
     A housing  11  of magnetic disk drive in a shape coefficient 3.5 inches mounts magnetic disk media  21  for a magnetic disk drive in a shape coefficient 2.5 inches, which aims a lightweighting of a rotational spindle portion, a decrease of a torque loss during on-load rotation with the media, and a decrease of a electric current into a spindle motor  41  during rotation.  
     Further, fins  11   a  for heat radiation may be arranged around the housing  11,  which results in avoidance or decrease raising a temperature in the housing  11.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] A present invention relates to a magnetic disk drive,particularly, rotating a magnetic disk medium in a high speed and amagnetic disk drive system using this technique.

[0003] 2. Description of the Related Art

[0004] In a magnetic disk drive system that is used as a high precisionexternal storage, for example, a computer, a file server or a diskarray, it is well known that by a magnetic head that flies with a givendistance over a recording surface of a magnetic disk medium in themagnetic disk drive system, a dedicated information is recorded on orreproduced from the magnetic disk medium via a magnetic flux.

[0005] A performance of magnetic disk drives greatly comes to decide athroughput of the magnetic disk drive system in the recent years. Forbetter performance, there are next universal aims in the improvement ofthe system.

[0006] 1) a memory capacity improvement within a limited system hardwareIncrease of an information storage capacity per unit volume)

[0007] 2) retrenchment of time for moving a magnetic head to a dedicatedtruck on the magnetic disk medium (Shortening of seek time)

[0008] 3) retrenchment of waiting time in rotation for waiting amagnetic head to a dedicated location at the specified position on atruck of the magnetic disk medium

[0009] These items were resolved in the present invention by an increaseof rotational speed of the magnetic disk media, which also increases aninput-output transfer rate of information between magnetic disk driveand upper system ,and between magnetic disk drive system and uppersystem.

[0010] There is a “3.5 inches” drive in short from the past. Here, “3.5inches” is called shape coefficient. “3.5 inches” size means a magneticdisk drive which has an about 4 inches (101.6 mm) in width, an about5.75 inches (146.1 mm) in length. It usually has an about 1 inch heightunless otherwise specified.

[0011] In case a rectangular parallelepiped circumscribes a magneticdisk drive, let's imagine the largest face that is parallel to themagnetic disk medium. At this time, the largest face of the “3.5 inches”drive can include two largest faces of a “2.5 inches” drive. Similarly,a largest face of the “5 inches” drive can include two largest faces ofa “3.5 inches” drive. The shape that falls in the above relationship,golden section, is called a form factor size.

[0012] The conventional “3.5 inches” magnetic disk drive has astructure, in a housing with 3.5 inches shape coefficient, whichcomprises: an arm than supports magnetic head parts, a carriage with thearm, which positions the magnetic head to the specified location on themagnetic disk media, an in-hub-type spindle motor that has rotationalmechanism within a hub that holds the magnetic disk media on its outersurface, and magnetic disk media of which most outside diameter is 95 mmstacked on the hub (hereinafter called “3.5 inches” disk for short).

[0013] Here, there are “3.5 inches” magnetic disk drives which havemainly about 1 inch (25.4 mm) height or about 1.63 inches (41.4 mm)height.

[0014]FIG. 3 shows an inner structure (plan view) of prior “3.5 inches”magnetic disk drive. External size of the housing 13 is a 3.5 inchesform factor size (101.6 mm×146 mm). Magnetic disk media 23 are securedby a disk clamp 33 to a spindle motor 43, which are rotated atpredetermined speed in this housing.

[0015] Magnetic heads 53 are secured to an edge of an actuator (thecarriage and a coil) 63. The actuator 63 is secured rotatably by a pivotbearing 73 to the housing. The housing 13 secures a voice coil motor 83that consists of a magnetic circuit. The coil of the actuator 63 isflowed by electricity, then it generates a rotational torque withelectromagnetic force and drives the actuator 63. Consequently, themagnetic head 53 supported at the edge of the actuator executes a seekoperation in which the head are located at an artbitrary location on thedisk media 23 along a quasi-radial direction.

[0016] In the 1.6 inches height magnetic disk drive with an about 41 mmofficial height, the spindle motor 43 is mounted stackingly with eight“3.5 inches” disk media (0.8 mm thickness). In 1 inch height magneticdisk drive with an about 25.4 mm official height, it is mountedstackingly with four “3.5 inches” disk media.

[0017] Other prior arts about faster rotating technique of spindlemotors are disclosed, for example, at Japanese Laid opened, sho63-104282 (corresponding to U.S. Pat. No. 5,243,479) and at JapaneseLaid opened, hei 04-205776 that shows stacking structures with “3.5inches” disk media or “2.5 inches” disk media in a housing of 5.25inches of shape coefficient.

[0018] Inventors of this application tried to rotate magnetic disk mediaof 1.6 inches height magnetic disk drive shown in FIG. 3 faster than inprior arts. They confirmed that when a rotational speed of spindle motor43 becomes 10000 rpm from 7200 rpm (prior rotational speed), electricenergy consumption increases with about 60 percent and becomes more than20 watts despite a lightweight design review that decreases the diskmedia 23 from 10 disks to 8 disks in the stack.

[0019] They also confirmed that an inner temperature of the housing 13becomes more than 80 degree centigrade without cooling means surroundingthe 1.6 inches height magnetic disk drive shown in FIG. 3. The coolingmeans are, for example, a fan that makes air flow for cooling.

[0020] Inventors of this application tried to rotate magnetic disk mediaof 1.6 inches height magnetic disk drive shown in FIG. 12 faster than inprior arts. When a rotational speed of spindle motor 43 becomes 12000rpm from 6300 rpm (prior rotational speed), electric energy consumptionincreases with about 460 percent.

[0021] Japanese Laid opened, hei 4-205776 shows a magnetic disk drivethat mounts a stack of magnetic disk media smaller in outer size thanthat of “5.25 inches” magnetic disk media within a housing that isdesigned for a 5.25 inches form factor size magnetic disk drive. But itdoes not consider an increase of heat generation caused from fasterrotation and higher density mounting.

[0022] Japanese Laid opened, sho 63-104282 (corresponding to U.S. Pat.No. 5,243,479) does not consider fully a heat radiation while itdiscloses an increase of rotational speed of magnetic media.

[0023] Inventors of this application mounts magnetic disk media for “2.5inches” form factor magnetic disk drives, in the housing for 1.6 inchesheight “3.5 inches” magnetic disk drive. And further they rotates themedia at 12000 rpm in order to fabricate a magnetic disk drive with ahigh transfer rate of information (FIG. 13, FIG. 14). Inventors of thisapplication found that it is necessary for keeping the inner temperatureequal to or lower than 60 degrees centigrade to mount eight disk mediaor less when 0.8 mm thickness media are adopted and to mount eleven diskmedia or less when 0.635 mm thickness media are adopted. That is, theyfound that it is possible to rotate disk media faster with victimizingthe information storage capacity in some extent, and that the storagecapacity and the faster rotation of the media are in the trade-offrelationship.

[0024] Here, disk media for the 2.5 inches form factor magnetic diskdrive have a 65±3 mm diameter (outermost diameter) and a 0.8 mm ±0.2 mmthickness or a 0.4 mm±0.2 mm thickness. Normal thicknesses of the mediaare 0.8 mm, 0.635 mm or 0.381 mm.

[0025] One of the reasons why the inner temperature of the housing(during a seek operation) is kept in the predetermined temperature orless, for example, 60 degree centigrade or less, is to get a long lifeof the disk drive by setting an enough margin in temperature for longlives of a lubricant on the disk media surface and a grease in bearingsof the spindle motor. Another is not to give a bad influence to a statusbetween the magnetic head and the magnetic disk media, and to a postureof a slider. Consequently, recording or reproducing with a informationto or from the disk media are not influenced badly. Thus, temperaturespecifications of the magnetic disk drive can be guaranteed.

[0026] Thus, inventors of this application found that it is necessaryfor making the stack of media lightweight, for achieving the fasterrotational speed of the media, and for keeping or increasing the storagecapacity, to attach a special cooling mechanism to the magnetic diskdrive.

[0027] In the magnetic disk drive system, for example, the file serveror the disk array, it is desirable for rotating the magnetic mediafaster and for keeping the system highly reliable that cooling meansshould be provided to the magnetic disk drive.

SUMMARY OF THE INVENTION

[0028] It is an object of the present invention to provide magnetic diskdrives with a big storage capacity and a high reliability, which rotatethe magnetic disk media at a high speed and which restrain heatgeneration grown out of the high speed rotation.

[0029] It is other object of the present invention to provide magneticdisk drives and magnetic disk drive systems with a big storage capacityand a high speed accessing ability.

[0030] It is other object of the present invention to provide magneticdisk drives and magnetic disk drive systems with a high speed accessingability and a good cost performance.

[0031] Other objects of the present invention may be clear from thestatement of this specification and drawings.

[0032] Achieving the above objects, the magnetic disk drive of thepresent invention mounts magnetic disk media smaller in diameter than“3.5 inches” magnetic disk media within a magnetic disk drive in a shapecoefficient 3.5 inches. For more cost performance, (in other words,using general-purpose parts that do not come expensive in stead ofcustom-order parts), the magnetic disk drive of the present inventionmay mount magnetic disk media for drives in a shape coefficient 2.5inches, 65 mm media in outer diameter within the magnetic disk drive inthe shape coefficient 3.5 inches.

[0033] Under the above structure, in the housing that is sealedincluding the actuator, the spindle motor, etc., around the magneticdisk media of 65 mm in outer diameter, space of 95 mm−65 mm=30 mmarises. If it says in the distance from the center axis of the spindlemotor that rotates the magnetic disk media, a clearance of 15 mm arises.

[0034] From the trade off relationship between a performance and a priceof the magnetic disk drive, members for heat radiation may be arrangedin this margin area. Or this radiation member may not be arranged,resulting in that the magnetic disk drive may have a margin for parts'arrangement in the above space.

[0035] When the radiation members are arranged, they are composed toarrange fins (uneven parts) in surrounding periphery of the magneticdisk medium.

[0036] Distance between the center of the spindle motor that rotatesmagnetic disk media of 65 mm in outer diameter, and the center of theactuator, may be arranged so that it becomes 40±1 mm or less. Further,if cost performance is pursued, if normal actuator parts are used, andif a torque of the voice coil motor is increased, the above distance canbe extended to 47.5 mm. The distance may have a margin considering to awindage loss, etc..

[0037] Further, in stead of magnetic disk media of a 65 mm in outerdiameter, a magnetic disk media for a magnetic disk drive in a shapecoefficient 1.8 inches, may be used in the 3.5 inches magnetic diskdrive. The magnetic disk media of 48 mm in outer diameter are normalmedia for magnetic disk drives in shape coefficient 1.8 inches, and itsthickness is 0.381 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a cross-sectional side view of a magnetic disk drive,which shows a first embodiment of the present invention.

[0039]FIG. 2 shows a plan view of FIG. 1.

[0040]FIG. 3 shows a plan view of prior magnetic disk drive.

[0041]FIG. 4 shows an oblique view of a magnetic disk medium which has2.5 inches form factor size in 0.381 mm thickness.

[0042]FIG. 5 shows an oblique view of a magnetic disk medium which has1.8 inches form factor size in 0.381 mm thickness.

[0043]FIG. 6 shows a plan view of magnetic disk drive that is the secondembodiment of present invention.

[0044]FIG. 7 is a cross sectional view between A-A portion that shows afin shape in FIG. 6.

[0045]FIG. 8 is the second cross sectional view between A-A portion thatshows a fin shape in FIG. 6.

[0046]FIG. 9 is the third cross sectional view between A-A portion thatshows a fin shape in FIG. 6.

[0047]FIG. 10 shows a plan view of the third embodiment of presentinvention, which is a magnetic disk drive higher than a normal height.

[0048]FIG. 11 shows a cross-sectional side view of FIG. 10.

[0049]FIG. 12 is a cross-sectional side view of a magnetic disk drive,which shows the fourth embodiment of the present invention.

[0050]FIG. 13 is a side view in depth direction of FIG. 12.

[0051]FIG. 14 is a side view in depth direction of the fourthembodiment, which shows an air flow.

[0052]FIG. 15 is a side view in width direction of FIG. 12.

[0053]FIG. 16 is a deformed side view in width direction of FIG. 12.

[0054]FIG. 17 is a side view in depth direction of a magnetic disk drivethat shows the fifth embodiment of present invention.

[0055]FIG. 18 is an oblique view of a magnetic disk drive which showsthe fourth embodiment of present invention.

[0056]FIG. 19 is a cross sectional side view of the sixth embodiment ofpresent invention, which shows a magnetic disk drive higher than normal.

[0057]FIG. 20 is a side view in depth direction of a magnetic disk drivethat shows the seventh embodiment of present invention.

[0058]FIG. 21 is a side view in depth direction of a magnetic disk drivethat shows the eighth embodiment of present invention.

[0059]FIG. 22 is a side view in width direction of a magnetic disk drivethat shows the ninth embodiment of present invention.

[0060]FIG. 23 is a side view in depth direction of a magnetic disk driveshown in FIG. 22.

[0061]FIG. 24 is a side view in depth direction of a magnetic disk driveshown in FIG. 22.

[0062]FIG. 25 is an architecture of a magnetic disk drive system thatmounts the magnetic disk drive of present invention.

[0063]FIG. 26 is an oblique view of a magnetic disk drive of the fourthembodiment of present invention, which shows a different spacing inparts-arrangement from a normal magnetic disk drive.

[0064]FIG. 27 shows a plan view of FIG. 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065]FIG. 1 is a cross-sectional view that shows an outline of theinternal structure of the magnetic disk drive, first embodiment of thepresent invention. Housing 11 has a 3.5 inches form factor size withofficial height of 41.4 mm. “2.5 inches” magnetic disk media 21 (65 mmin diameter, 0.635 mm in thickness), a spindle motor 41 that rotatesthese media 21 in a predetermined rotational speed, a rotary typeactuator 61 that locates the magnetic head around a pivot bearing 71,and a voice coil motor 81 that drives the rotary type actuator 61 aresecured in this housing 11.

[0066] A securing method of the spindle motor 41 is with a screw or by apress fit to be secured at one edge of or at both edges of the spindlemotor 41 to the housing 11 that includes the spindle motor 41, or to thehousing 11 and a cover 101 that hermetically closes the inner space ofthe housing 11. Magnetic disk medium 21 uses Al (aluminum) or glass forits substrate material. For more economic fabrication of the magneticdisk drive, in place of screws and press fits, an adhesive may be usedfor securing.

[0067] Magnetic disk media 21 are stacked via spacers 141, thickness ofwhich is 1.7 mm. The space between the media is 1.7 mm. 12 media arestacked in an axial direction. Magnetic disk media 21 are fixed by adisk clamp 31 to the spindle motor 41 that can rotate to 15000 rpm.

[0068] The 111 axis of the rotary center of magnetic disk media 21 isarranged almost at a central portion of the housing 11. The housing 11that is en bloc casted with aluminum alloy, has linear fins 11 aarranged at four portions outside the housing, each of which fins isdefined with a thickness at a leaf edge t=2 mm, a leaf length L=32 mm, adistance H between leaf edges is 5 mm, and each of which fins is stoodstraight against 111 axis of the rotary center of magnetic disk media21.

[0069] As magnetic disk media 21 becomes smaller in diameter, forexample, as changing “3.5 inches” disk media to “2.5 inches disk mediain same thickness of 0.8 mm, a weight per one disk medium reduces byabout 54%. As changing “3.5 inches” disk media to 2.5 inches” disk mediain other thickness of 0.635 mm, a weight per one disk medium reduces byabout 64%. Therefore, a gross weight the spindle motor rotates can bereduced, which brings a high characteristic at a spin-up operation, andwhich also effects a reduction of electric current (electric energyconsumption during an idle rotation.

[0070] If magnetic disk media are changed from “3.5 inches” to “2.5inches”, for example, a maximum marginal velocity when the “3.5 inches”disk media rotate at 10000 r.p.m. equals to a maximum marginal velocitywhen the “2.5 inches” disk media rotate at 14600 r.p.m. Therefore, whenrecording or reproducing an dedicated information to or from themagnetic disk media 21 by a magnetic head 51 (FIG. 2) via a magneticflux, if a signal processing ability is same as in the past or more,faster rotation of the media can be executed without a reduction ofrecording density in longitudinal direction along a track that islocated concentrically on the magnetic disk media 21.

[0071] When magnetic disk media 21 rotate, they receive a frictionalresistance by a viscosity of air that surrounds the magnetic disk media21. A transition boundary where an air flow along a surface of themagnetic disk media becomes from a laminar flow to a turbulent flow isabout 15000 r.p.m. when the magnetic disk media 21 is “3.5 inches” diskand about 30000 r.p.m. when the media is “2.5 inches” disk.

[0072] When magnetic disk media 21 are changed from “3.5 inches” to “2.5inches”, the transition boundary is big enough against the number ofrotation limits of the spindle motor 41. Because an torque loss duringon-load rotation, which is caused from the frictional resistance,becomes bigger biquadrately proportional to a diameter of the magneticdisk media, if the spindle rotates the media in a same speed, the torqueloss of “2.5 inches” disk media corresponds to about 22 of that of “3.5inches” disk media. Therefore, when the spindle motor 41 rotates in apredetermined idle speed, the current (consumption power) becomessmaller, and a heat generation caused by windage can be restrained.

[0073] Fins 11 a are made at plural portions of the housing 11, whichhave an effect that increases a surface area of the housing 11 and thatmakes a heat-penetration flow good. The tips of fins 11 a become closerto the temperature of the external air of housing 11. The rotation ofspindle motor 41 and the flutter of actuator 61 driven by the systemgenerate a heat, which rises an internal temperature of the magneticdisk drive. The fins 11 a reduce this temperature increase.

[0074] As for the fins, if the thickness t is 0.5 mm or more, aradiation coefficient almost never changes. If the length L of the finsat four portions is made to be 10 mm or more , the radiation becomeseffective. Consequently, the fins can restrain temperature risings atleast with about 5 degree centigrade at 10000 r.p.m. rotation, about 8degree centigrade at 12000 r.p.m. rotation, and about 10 degreecentigrade at 15000 r.p.m. rotation. It is advantageous to make thelength L of the fins long as much as possible. And it can bring a heatpenetration flow good to make the number of the fins big as many aspossible, because the surface area of the fins become broader. And ifthe fins 11 a are arranged in a air flow made by a fan that is installedin a case of a magnetic disk drive system on which the magnetic diskdrive is mounted, a cooling of the magnetic disk drive become moreeffective.

[0075] a) Power consumption (during the idle rotation) can be restrainedas 6.3 watt or less when the spindle rotates at 10000 r.p.m., 8.3 wattor less when it rotates at 12000 r.p.m., and 11.8 watt or less at 15000r.p.m.

[0076] b) The inner temperature of the housing 11 (during the seekoperation) can be restrained at 47 degree centigrade or less when thespindle rotates at 10000 r.p.m., at 52 degree centigrade or less when itrotates at 12000 r.p.m., and at 58 degree centigrade or less at 15000r.p.m.

[0077] Finally, the inner temperature of the housing 11 during the seekoperation can be at 60 degree centigrade or less under the conditionthat the magnetic disk media are twelve, the magnetic disk drive isinstalled in the magnetic disk drive system without fan.

[0078] The conditions under which the above numerals are obtained are asfollows: the medium is a “2.5 inches” (diameter: 65 mm, thickness: 0.635mm), the stack has twelve media, the distance between media is 1.7 mm, Lof fins=32 mm , the thickness t of the fins=2 mm, a circumferentialtemperature of the magnetic disk drive is 25 degree centigrade, themagnetic disk drive system has no fan.

[0079] The magnetic head 51 and an arm of the actuator 61 receive aforce from a homogeneity air flow that is generated by rotation of themagnetic disk media. If the force which is received by the actuator 61including the magnetic head 51, from the air flow can be decreased, thetorque loss during on-load rotation of the magnetic disk media 21further can be decreased, which results in suppressing the heatgeneration caused by windage.

[0080]FIG. 2 shows a plan view of an arrangement with basic elementaryparts in the magnetic disk drive shown in FIG. 1.

[0081] A distance B between a rotation center 111 of the magnetic diskmedia 21 and a rotation center 121 of the magnetic head 51 can bereduced comparing with the prior magnetic disk drive shown in FIG. 3because the magnetic disk media 21 become smaller in diameter. Namely,if the distance B of them is set with 40 mm (FIG. 2), a gap on themagnetic head 51, which records or reproduces an information on or fromthe magnetic disk media 21, can be arranged at R=37.5 mm location fromthe rotation center 121. Incidentally, a corresponding distance B in theprior magnetic disk drive shown in FIG. 3, which is defined as adistance between a rotation center 113 of a magnetic disk media 23 and arotation center 123 of a magnetic head 53, is 54 mm. Because themagnetic disk media 21 become smaller in diameter than prior media 23, asurrounding space of the media has a clearance with 15 mm. Therefore, 54mm−15 mm =39 mm may be adopted as the distance B of FIG. 2. 40 mm±1 mmas the distance B seems to be realistic value considering a tolerancefor fabrication.

[0082] Further, considering to use existing standard parts of theactuator for fabricating economic magnetic disk drives, the distance Bof FIG. 2 may be 47.5 mm=the above R+10 mm. A deterioration in accessspeed should be compensated by increasing the torque of the voice coilmotor in this case.

[0083] Present invention described above can make an actuator portionsmaller and lighter than the prior actuator 63 including the magnetichead 53. More specifically, a weight of rotational portion at theactuator 61 including the magnetic head 51 (FIG. 2) is about 32 gf(gram-force) to 36 gf, and a moment of inertia of the rotational portionat the actuator 61 including the magnetic head 51 is about 5200gf.square mm to 5800 gf.square mm. In the prior magnetic disk drivecorresponding to FIG. 2, a weight or a moment of inertia of rotationalportion at the prior actuator 63 are 45 gf or 14400 gf.square mm,respectively.

[0084] Applying the present invention, that is, in case the voice coilmotor that gives an output power of 0.2 N.m per one ampere current inthe prior magnetic disk drive of FIG. 3, is used for a voice coil motor81 that drives an actuator 61, an average access time can be decreasedto be about 6 milli-seconds in the magnetic disk drive. Here, theaverage access time defines an average time for the magnetic head 51 tobe located from a start track to a destination track which are arrangedconcentrically on the magnetic disk media 21. Incidentally, twelvemagnetic disk media 21 are used in this case, the rotational speed ofthe spindle is 10000 r.p.m. Inventors of present invention confirmed ifthe weight of rotational portion at the actuator 61 is smaller than 36gf, or if a torque of the voice coil motor is bigger than 0.12 N.m perone ampere current, the average access time can be reduced more smaller.When the weight of rotational portion at the actuator 61 is smaller than36 gf, and when the torque of the voice coil motor is 0.12 N.m per oneampere current, the average access time can be reduced by about 7milli-seconds.

[0085] An actuator using the voice coil motor that has a torque of 0.12N.m per one ampere current, gave 6.5 milli-seconds during a readoperation, 7.5 milli-seconds during a write operation in average accesstimes, respectively (in the third embodiment of present invention; aweight of rotational portion at the actuator is 53.0 gf.).

[0086]FIG. 4 shows a size of a magnetic disk medium which has 2.5 inchesdiameter and 0.381 mm thickness. FIG. 5 shows a size of a magnetic diskmedium which has 1.8 inches diameter and 0.381 mm thickness. It givessurely above described same effects to exchange these disk media 24, 25different in size, for magnetic disk media 21 shown in FIG. 1, and tomount them in the magnetic disk drive.

[0087]FIG. 6 shows a plan view of the second embodiment of presentinvention, a magnetic disk drive which has 41.4 mm or 1.6 inches nominalheight and 3.5 inches form factor size. FIG. 7 shows across sectionbetween A-A portion in FIG. 6.

[0088] The feature of this embodiment is that the magnetic disk drivearranges fins on all sides of housing 16 as same as shown in FIG. 1, andthat the fins on one side consist of 4 linear fins 16 a arranged at 4 mminterval, each fin has 3 mm thickness at the edge and 12 mm length, asshown in FIG. 7. Ten magnetic disk medium 26 (FIG. 6), each of which has65 mm in diameter and 0.8 mm in thickness, are accommodated at thehousing at 1.84 mm interval (FIG. 7). They are secured to a spindlemotor 36 (FIG. 6) that can drive them at 12000 r.p.m. rotational speed.A maximum temperature (during seek operation) in the housing 16 is heldat 55 degree centigrade or less and an electric power consumption is 8.7watts during an idle rotation in the above case. Incidentally, anenvironmental temperature of the magnetic disk drive is 25 degreescentigrade and there is no fan on a case frame of the magnetic diskdrive system.

[0089]FIG. 8 and FIG. 9 show other shapes of fins. FIG. 8 shows a crosssection between A-A portion in FIG. 6 when fins 16 b are arranged insidethe housing 16. FIG. 9 shows a cross section between A-A portion in FIG.6 when fins 16 c and 16 d are arranged inside and outside the housing16.

[0090]FIG. 10 and FIG. 11 show the third embodiment of presentinvention, a “3.5 inches” magnetic disk drive which has 68 mm height.This is higher than a normal height of 3.5 inches standard.

[0091] Fifteen magnetic disk media 22, each of which is 65 mm indiameter and 0.8 mm in thickness, are stacked to a hub 162 at 2 mminterval with interjacent disk spacers 142 that is 2 mm in thickness(FIG. 11). Here, for example, means (a spindle motor) capable forrotating the magnetic disk media 22 at 12000 r.p.m. rotational speed,equip its coil 202, stator core 192 and magnet 212 outside the housingin the rotational axis direction of hub 162.

[0092] There are five fins 12 a at 5 mm interval on one side of thehousing 12. An edge portion of the fin 12 a is 2 mm in thickness. Alength of the fin is 32 mm. PCB (printed circuit board) 152 adoptsSCSI-2 interface(s) and it has terminals for supplying electric powerwith voltages, 12 volt and 24 volt. The terminals are arranged with aclearance, about 7 mm toward the housing 12. Here, these voltages areexemplifications. If a desirable rotational speed is obtained, othervoltages except 12 volt or 24 volt are available. Some value in voltagemay be adopted, which is decided by characteristic of a spindle motor.

[0093] Features of this embodiment are as follows:

[0094] 1) this magnetic disk drive adopts a spindle motor locatedvertically under the housing 12 in FIG. 11, which is called a bottomtype spindle motor and which rotates inner wheels of bearings 182 a and182 b in order to avoid a leakage of magnetic fluid sealants and anabrasion of bearings which are caused from a high speed rotation of thespindle motor and the magnetic disk media. Consequently, the bottom typespindle motor does not affect badly to a grease in the bearings and themagnetic fluid sealants 222 a, 222 b;

[0095] 2) this magnetic disk drive adopts a high voltage of the electricpower supply which gives an enough rush current to spin up the spindlemotor and which compensates a voltage drop in a driving circuit. Thespindle motor can rotate stably in high speed owing to an enough torquefor rotating the magnetic disk media.

[0096] PCB 152 is arranged with a clearance, about 7 mm toward thehousing 12 to restrain a temperature rising of the magnetic disk drive,which is caused by a heat generation of the PCB. Consequently, themagnetic disk drive of this embodiment gives 1) 6 giga-bytes informatted storage capacity, 2) 10 watts electric power consumption orless, 3) 55 degree centigrade in inner temperature of the housing 12(during seek operation) when an environmental temperature of themagnetic disk drive is 25 degrees centigrade and there is 2 meters persecond of a cooling air flow caused by fans on a case frame of themagnetic disk drive system. Incidentally, a transfer rate from themagnetic disk drive to an upper system is 10 mega-bytes per second ormore. Data transfer rate is expected to be increased more by anoptimization of electric circuits.

[0097] Regardless of this embodiment, if coil 202 and stator core 192 ofthe spindle motor and all the like driving means there, are arranged farenough from exterior of the housing 12, and if the clearance between PCB152 and the housing 12 is set in 10 mm or more, the temperature risingof the magnetic disk drive can be further restrained.

[0098]FIG. 12 is a cross-sectional view that shows an outline of theinternal structure of the magnetic disk drive, fourth embodiment of thepresent invention. A housing 11 and a cover 101 are sized in a 3.5inches form factor which has a nominal height of 41.4 mm. “2.5 inches”magnetic disk media 21 (65 mm in diameter and 0.8 mm in thickness), aspindle motor 41 that rotates these media in a predetermined rotationalspeed, a rotary type actuator 61 that swings around a pivot-bearing 71for positioning magnetic heads, and a voice coil motor 81 that drive theactuator, are secured in the housing 11.

[0099] A securing method of the spindle motor 41 is with a screw or by apress fit to be secured at one edge of the spindle motor 41 to thehousing 11 that includes the spindle motor 41. The other edge of thespindle motor 41 is secured at a cover 101 that hermetically closes theinner space of the housing 11. Magnetic disk medium 21 uses Al(aluminum) or glass for its substrate material.

[0100] Ten magnetic disk media 21 are stacked in a rotational axisdirection at 1.84 mm interval with interjacent disk spacers 141 that is1.84 mm in thickness. The magnetic disk media 21 are secured by a diskcramp 31 to the spindle motor 41 that can rotates in a rotational speedof 12000 r.p.m. The housing 11 casted with an aluminum alloy has en bloclinear fins 11 a stood straight against 111 axis of the rotary center ofmagnetic disk media 21. The thickness at the leaf edge t=2.5 mm, theleaf length L=12 mm, a distance H between leaf edges is 3.5 mm.

[0101] If the housing is casted en bloc, a thickness of the housingprefers to be kept 1.5 mm or more in order to give a smooth-running withmelting materials during the casting and to uniform mechanical orphysical characteristics of a casted product. The product needs taperportions in case it is locked inside a casting flask by a shrinkage thatfollows a cooling of the product when the product is separated from thecasting flask. The amount of the taper is about 1 degree in angle. If anedge of fin that has 12 mm in length is 1.5 mm in thickness, a basalthickness of the fin is 1.9 mm. If an edge has 15 mm in length, a basalthickness of the fin is about 2 mm.

[0102] As magnetic disk media 21 becomes smaller in diameter, forexample, as changing “3.5 inches” disk media to “2.5 inches” disk mediain same thickness of 0.8 mm, a weight per one disk medium reduces byabout 54%. In other thickness of 0.635 mm, as changing to “2.5 inches”disk media, the weight per one disk medium reduces by about 64%.Therefor, a gross weight that the spindle motor rotates can be reduced,which brings a high characteristic at a spin-up operation, and whichalso effects a reduction of electric current (electric energyconsumption) during an idle rotation.

[0103] If magnetic disk media are changed from “3.5 inches” to “2.5inches”, for example, a maximum marginal velocity when the “3.5 inches”disk media rotate at 10000 r.p.m. equals to a maximum marginal velocitywhen the “2.5 inches” disk media rotate at 14600 r.p.m. Therefore, whenrecording or reproducing an dedicated information to or from themagnetic disk media 21 by a magnetic head 51 via a magnetic flux, if asignal processing ability is same as in the past or more, fasterrotation of the media can be executed without a reduction of recordingdensity in longitudinal direction along a track that is locatedconcentrically on the magnetic disk media 21.

[0104] When magnetic disk media 21 rotate, they receive a frictionalresistance by a viscosity of air that surrounds the magnetic disk media21. A transition boundary where an air flow along a surface of themagnetic disk media becomes from a laminar flow to a turbulent flow isabout 15000 r.p.m. when the magnetic disk media 21 is “3.5 inches” disk,and about 30000 r.p.m. when the media is “2.5 inches” disk.

[0105] When magnetic disk media 21 are changed from “3.5 inches” to “2.5inches”, the transition boundary is big enough against the number ofrotation limits of the spindle motor 41. Because an torque loss duringon-load rotation, which is caused from the frictional resistance,becomes bigger square or cubicly proportional to a diameter of themagnetic disk media, if the spindle rotates the media in a same speed,the torque loss of “2.5 inches” disk media corresponds to about 50%˜34%of that of “3.5 inches” disk media. Therefore, when the spindle motor 41rotates in a predetermined idle speed, the current (consumption power)becomes smaller, and a heat generation caused by windage can berestrained. Fins 11 a are made at plural portions of the housing 11,which have an effect that increases a surface area of the housing 11 andthat makes a heat-penetration flow good. The tips of fins 11 a becomecloser to the temperature of the external air of housing 11. Therotation of spindle motor 41 and the flutter of actuator 61 driven bythe system generate a heat, which rises an internal temperature of themagnetic disk drive. The fins 11 a reduce this temperature increase.

[0106] The thickness of the fin at the edge or tip may be 1.5 mm ormore, considering its easier fabrication. If a length of the fin iselongated, a surface area of the fin becomes larger. A temperature of anair that flows along the fin increase because a heat from the fin and aheat by a viscosity resistance are conducted to the air. Therefore thefin should be divided into plural portions. FIG. 13 shows shapes of finsdivided into three d 11 b, 11 c, 11 d in a depth direction of themagnetic disk drive.

[0107] Here, a height direction is defined to be called a thicknessdirection if the magnetic disk drive stands as a rotational axis of itshub is vertical. A longer side is defined to be called a depth directionand a shorter side, a width direction if the magnetic disk drive is seenfrom a bird's-eye view. These divided fins are arranged like steps ofstairs, which change in position in the thickness direction.

[0108] The fins are located in a space that is surrounded by a base(housing) 11, a mounting portion 11 g which mounts a cover 101 and amounting portion 11 h which mounts a circuit board. This space alsoforms a pass for an air flow 300 shown in FIG. 14.

[0109] Fins 11 a, 11 b, 11 c and 11 d have a function that can enhance acooling efficiency of the magnetic disk drive about air flows those areshown by arrow marks 300, 301 and 302 in FIG. 14 and FIG. 18. Theportion of the fins, which encounters with the air flow is cooled bestin the air flow. The cooling efficiency decreases for the air's goingdownstream from the encounter portion owing to a development of aboundary layer. Therefore the best efficiency about the air flow isgiven by a bossy fin.

[0110] On the other hand, a radiation area decides a cooling efficientif there is no air flow. Therefore, a strap shape fin is effective inthis case. Further, if it is considered to assemble or to cast en blocwith the housing 11 and fin 11 a etc. of the magnetic disk drive,practical shapes of the fins those have good cooling efficiency are, asshown in present embodiments, plural sets of short strap shape fins,which are arranged surrounding the magnetic disk drive.

[0111] It is desirable for fins and air flow to encounter or to collideeach other as possible as they can. And it is necessary to keep anenergy loss of the air flow small, to maintain the air-current speed andto hold the pass open. It is also a desirable configuration of the finto have smooth roundness at the corners (air-collision portion) thatdirectly encounter the air flow in order to keep the loss of air flowsmall and to maintain the cooling efficiency high when the air flowcollides with the corners.

[0112] Therefore in present invention that takes the above phenomenoninto consideration, plural strap-shape fins are arranged changing inposition in the thickness direction. That is, FIG. 14 shows the air flow300 comes from left hand. Some air flow shown as short arrow 300 acollides with a round portion 11 b′ of leading edge of the fin one afteranother, cooling the leading edge preferentially and going through toright hand of FIG. 14.

[0113] Passes shown as long arrows 300 b are arranged for some other airflow besides the collision air in order to keep the air-current speed.Consequently, among width-direction fins 11 a and depth-direction fins11 b, 11 c and 11 d (FIG. 13), neighbor sets of fins differ in height(location in the thickness direction) and are arranged changing in theirheights one after another.

[0114]FIG. 15 shows one set of fin 11 a in the width direction and therow is one column (set) because a flask is used to form the fins by enbloc casting. So called sliding cores those separate in bidirectionally,right and left respectively, form fins in the depth direction and in thewidth direction. Right and left sliding cores meet at a center portion(11 f) of fins in the width direction and form the fins 11 a. Inseparation, each of the sliding cores goes along the arrow 400, 401shown in FIG. 15, respectively, and the product is released.

[0115] Fins 11 a in the width direction become a single row fins whenthe roundness of their corners are formed by casting. At most two rowfins (FIG. 16) changing in their heights can be fabricated when theroundness of their corners are worked afterwards without casting. Aparting face (separation face) of the sliding cores defines a boundarybetween the two row fins. The fins in present invention can reserveabout 70,000 square milli-meter or more as the surface area of themagnetic disk drive.

[0116] Further explanation about the flask is complemented using FIG.15. A flask for casting the base 11 consists of a normal main flasksthose separate up-and-down direction of FIG. 15 and sliding cores thoseform fins 11 a, 11 b. The sliding cores slide in predetermineddirections accompanying with a separating operation of the normal mainflasks. The sliding cores may consist of three members or more in orderto form fins in a predetermined shape. On the other hand, the slidingcores may be two members according to a heat generation of the magneticdisk drive or to keep a freedom in fabrication of the mounting portionthat mounts a circuit board.

[0117]FIG. 18 shows a varied embodiment which is increased in height ofmounting portion 11 g that mounts cover 101 to base (housing 11),satisfying 3.5 inches form factor size. In this embodiment:

[0118] a) an electric power consumption (during an idle rotation loaded10 disk media can be restrained as 5.5 watts at 10,000 r.p.m. rotationalspeed, and 7.0 watts at 12,000 r.p.m. rotational speed;

[0119] b) a temperature rising (during following operation, anenvironmental temperature is 32 degrees centigrade) can be restrained at40 degrees centigrade or less at 12,000 r.p.m. rotational speed. Withouta cooling air flow, it can be restrained at 46 degrees centigrade orless at 10,000 r.p.m. rotational speed, at 52 degrees centigrade or lessat 12,000 r.p.m. rotational speed.

[0120] The numerals above described are obtained under the conditionthat ten “2.5 inches” media (65 mm in diameter, 0.635 mm in thickness)are installed at 1.84 mm interval in a magnetic disk drive with finsthose are 12 mm in length and 2 mm in thickness. And that anenvironmental temperature of the magnetic disk drive is 32 degreescentigrade and there is no cooling air flow caused by fans on a caseframe of the magnetic disk drive system.

[0121] The magnetic head 51 and an arm of the actuator 61 receive aforce from a homogeneity air flow that is generated by rotation of themagnetic disk media. If the force which is received by the actuator 61including the magnetic head 51, from the air flow can be decreased, thetorque loss during on-load rotation of the magnetic disk media 21further can be decreased, which results in suppressing the heatgeneration caused by windage.

[0122]FIG. 17 shows fifth embodiment of the present invention. Namely, acover mounting portion 11 g is extended upwards to be 41.4 mm, airpasses are enlarged and numbers of fins are increased.

[0123]FIG. 19 shows sixth embodiment of the present invention, 68 mmheight “3.5 inches” magnetic disk drive, which has a larger height thannormal “3.5 inches” standard. Fifteen magnetic disk media 22 are stackedon a hub 162 at 2 mm interval with interjacent disk spacers 142 (FIG.19) that is 2 mm in thickness. Here, for example, means (a spindlemotor) capable for rotating the magnetic disk media 22 at 12000 r.p.m.rotational speed, equip its coil 202, stator core 192 and magnet 212outside the housing in the rotational axis direction of hub 162. Thereare five fins 12 a at 6 mm interval on one side of the housing 12. Anedge portion of the fin 12 a is 2 mm in thickness. A length of the finis 32 mm.

[0124] PCB (printed circuit board) 152 adopts SCSI-2 interface(s) and ithas terminals for supplying electric power with voltages, 12 volt and 5volt. Features of this embodiment are as follows.

[0125] 1) this magnetic disk drive adopts a spindle motor locatedvertically under the housing 12 in FIG. 19, which is called a bottomtype spindle motor and which rotates inner wheels of bearings 182 a and182 b in order to avoid a leakage of magnetic fluid sealants and anabrasion of bearings which are caused from a high speed rotation of thespindle motor and the magnetic disk media. Consequently, the bottom typespindle motor does not affect badly to a grease in the bearings and themagnetic fluid sealants 222 a, 222 b;

[0126] 2) this magnetic disk drive adopts a high voltage of the electricpower supply which gives an enough rush current to spin up the spindlemotor and which compensates a voltage drop in a driving circuit. Thespindle motor can rotate stably in high speed owing to an enough torquefor rotating the magnetic disk media.

[0127] PCB 152 is arranged with a clearance, about 7 mm toward thehousing 12 to restrain a temperature rising of the magnetic disk drive,which is caused by a heat generation of the PCB 152.

[0128] Consequently, the magnetic disk drive of this embodiment gives 1)15 giga-bytes in formatted storage capacity, 2) 14 watts electric powerconsumption or less, 3) a transfer rate from the magnetic disk drive toan upper system is 10 mega-bytes per second or more.

[0129] Data transfer rate is expected to be increased more by anoptimization of electric circuits. Regardless of this embodiment, ifcoil 202 and stator core 192 of the spindle motor and all the likedriving means are arranged far enough from exterior of the housing 12,and if the clearance between PCB 152 and the housing 12 is set in 10 mmor more, the temperature rising of the magnetic disk drive can befurther restrained.

[0130]FIG. 20 shows seventh embodiment of the present invention, thatis, a magnetic disk drive mounted directly with a cooling fan 400. Thecooling fan 400 is driven by a circuit board (PCB, printed circuitboard). As shown in Figure, the cooling fan 400 is arranged in order tomake an air flow through above described air passes, which aresurrounded by a cover mounting portion 11 g and circuit board mountingportion 11 h. The direction of the air flow by the cooling fan 400 maybe variable.

[0131]FIG. 21 shows the eighth embodiment of present invention.

[0132] In this magnetic disk drive, a magnetic disk head 56 is socorrectly positioned that positioning servo signals are written onmagnetic disk media 21 before the magnetic disk drive is shipped.

[0133] The writing of the servo signals are performed after a base(housing 11), a cover 101, disk media 21, spindle motor 41 or the likeof structural parts are assembled. It needs a reference signal to writethe servo signals. The magnetic disk drive needs a hole 11 e throughwhich the reference signal is provided. The hole 11 e needs to bearranged on a side of the base (housing 11). So, it is necessary forforming the hole 11 e to use sliding cores in casting flask. The slidingcores can make the fins 11 a and the hole 11 e on a same face, whichmakes the housing 11 formation (casting fins 11 a etc. en bloc) moreeasy.

[0134]FIG. 22 shows the ninth embodiment of present invention.

[0135] Fins 11 a in the width direction are extended further. A portionof them reaches side faces in the depth direction shown in FIG. 23 andFIG. 24. In this embodiment that increase a surface area, dividingcasting flasks (sliding cores) into right and left directions can formfins 11 a.

[0136]FIG. 25 shows a schematic of a magnetic disk drive system or adisk array system, which connects a plurality of magnetic disk drive 230that is explained in FIG. 1, FIG. 6, FIG. 10 and FIG. 11.

[0137] The magnetic disk drive system sets a case 240 that mounts orsecures plural magnetic disk drives 230, and a control unit 250 withinthe case. The control unit 250 couples electrically the plural magneticdisk drives 230 and controls them. Further the magnetic disk drivesystem sets fans 260 that refrigerate the control unit 250 and theplural magnetic disk drives 230. The fan 260 can be omitted iftemperature circumstances surrounding the system at a installation placeare favorable or if a number of magnetic disk drives mounted on thesystem is small enough. The fans 260 may be arranged for cooling pluralmagnetic disk drives mainly. Special fans 260 may be arranged for thecontrol unit 250.

[0138] Control unit 250 mainly receives data from or transmits data toplural magnetic disk drives, the magnetic disk drive system or the uppersystem that uses the magnetic disk drives or the magnetic disk drivesystem, and mainly administer control information.

[0139] When an air flow by the fan 260 is 2 meter per second, a maximumtemperature (during seek operation) in the housing of the magnetic diskdrive 230 is held at 55 degree centigrade or less. Here, parametersaround this magnetic disk drive are as follows: magnetic disk media havea 65 mm in diameter for “2.5 inches” size and a 0.8 mm in thickness; aninterval or a distance of the media is 2.0 mm; a length of fins arrangedaround the media is 32 mm and a thickness of the fins is 2 mm, a numberof leaves in magnetic disk media is 15; a rotational speed of a spindlethat rotates the media is 12000 r.p.m.; an electric power consumption is10 watts during an idle rotation in the above magnetic disk drive; adistance between a hub center and an actuator center is 43.2 mm; and aweight of rotational portion at the actuator is 53.0 gf.

[0140]FIG. 26 and FIG. 27 show the tenth embodiment of presentinvention, 1.6 inches height “3.5 inches” magnetic disk drive.

[0141] A housing 2 is 3.5 inches form factor size which has a nominalheight of 25.4 mm. The housing mounts magnetic disk media 4, a spindlemotor (not shown) rotating the media in a predetermined speed, a swingtype actuator 13 positioning a magnetic head 11 around a pivot bearing15, and voice coil motor that is a driving means for the actuator.

[0142] There are two securing embodiments: one of a securing method ofthe spindle motor is with a screw or by a press fit to be secured at oneedge of the spindle motor to the housing 2 that includes the spindlemotor; the other of a securing method of the spindle motor is with ascrew or by a press fit to be secured at one edge of the spindle motorto the housing 2 that includes the spindle motor and the other edge ofthe spindle motor is secured at a cover that hermetically closes theinner space of the housing 2. Axes for the spindle motor and theactuator may be secured by glues or adhesives to the housing. Thissecuring method can bring more economical magnetic disk drives.

[0143] Features in this embodiment are: magnetic disk media 4 are madewith Al (aluminum) or glass and they are “2.5 inches” in diameter. Thesix magnetic disk media 4, each of which has 0.635 mm in thickness, aremounted axially with interjacent disk spacers those are each 1.7 mm inthickness. Magnetic disk media 4 are secured stably by a disk cramp 8and a screw 19. There is a space around the magnetic disk media 4. Thespace makes better a radiation characteristic in the housing 2, and thespace gives freedom for selecting parts used in the housing.

[0144] A distance between a rotation center 21′ of the magnetic disk 4and a rotary center 23′ of the magnetic head 11 is set up for 40 mm. Theactuator 13 is secured via the pivot bearing 15 to the housing 2. Thedistance can be set at most 47.5 mm (=R below described +10 mm) for moreeconomical structures of the magnetic disk drives, if existing actuatorparts are used and if the torque of the voice coil motor is increased.

[0145] If ‘2.5’ inches magnetic disk media of 0.8 mm in thickness areused in stead of ‘3.5 inches’ magnetic disk media of same thickness, theweight decreases by about 54% per one medium. If ‘2.5’ inches magneticdisk media of 0.635 mm in thickness are used in stead of ‘3.5 inches’magnetic disk media of 0.8 mm in thickness, the weight decreases byabout 64% per one medium. Owing to a decrease in total weight of themedia those are rotated by the spindle, there are effects on a highcharacteristic of a spin-up operation by the spindle motor, and also ona reduction of electric current (electric energy consumption) during anidle rotation.

[0146]FIG. 27 shows basic inner structure of present invention (in planview).

[0147] The distance L between the rotation center 21′ of the magneticdisk 4 and the rotary center 23′ of the magnetic head 11 can be setshorter than that of prior magnetic disk drives because the smallermagnetic disk media 4 are used than usual. A gap 25′ of the magnetichead 11 that records or reproduces information to or from the magneticdisk media 4, locates 37.5 mm (=R) from the rotary center 23′.

[0148] Thus in this embodiment, the parts can be freely arranged in thehousing. If a performance (mainly storage capacity) be sacrificed,inexpensive parts can be adopted. So, there is a effect on fabricationof magnetic disk drives or magnetic disk drive systems, which put a highspeed accessing function and an inexpensive device price into practice.

[0149] Because the present invention adopts using smaller magnetic diskmedia in form factor size than usual in a normal form factor sizemagnetic disk drive housing, or arranging fins (unlevel, washboard orjaggy portion) around the housing, prior problems those are generated ina high speed rotational technique can be resolved. And the magnetic diskdrive or systems using thereof can be realized, which spends lesselectric power and gives less heat generation than prior magnetic diskdrive, and which can indicate a high access performance with a highstorage capacity.

[0150] When the magnetic disk drive of present invention is used for adisk array system or other magnetic disk drive systems, it can replaceprior magnetic disk drive without adding a special cooling mechanism tothe prior systems. There is an effect on easily realizing to perform ahigh speed operation and a high function, and to increase a storagecapacity.

[0151] Having described a preferred embodiment of the invention withreference to the accompanying drawings, it is to be understood that theinvention is not limited to the embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

We claim:
 1. A magnetic disk drive, comprising: magnetic disk media recording information; a hub holding said magnetic disk media rotatablly; a spindle motor rotating said hub; a magnetic head recording or reproducing information to or from said magnetic disk media; an actuator holding and locating said magnetic head at a predetermined position on said magnetic disk media; and a housing in a shape of 3.5 inches form factor size, mounting said magnetic disk media, said hub, said magnetic head and said actuator; wherein said magnetic disk media held on said hub, are smaller in diameter than magnetic disk media those are used for 3.5 inches form factor magnetic disk drive.
 2. A magnetic disk drive according to claim 1, wherein said spindle motor rotates 10000 rpm or more.
 3. A magnetic disk drive according to claim 2, further comprising fins arranged around said magnetic disk media.
 4. A magnetic disk drive, comprising: magnetic disk media recording information; a hub holding said magnetic disk media rotatablly; a spindle motor rotating said hub; a magnetic head recording or reproducing information to or from said magnetic disk media; an actuator holding and locating said magnetic head at a predetermined position on said magnetic disk media; and a housing in a shape of 3.5 inches form factor size, mounting said magnetic disk media, said hub, said magnetic head and said actuator; wherein said magnetic disk media held on said hub, are not greater in diameter than shape-coefficient 2.5 inches' magnetic disk media.
 5. A magnetic disk drive according to claim 4, wherein said spindle motor rotates 10000 rpm or more.
 6. A magnetic disk drive according to claim 1, wherein said hub and said actuator are arranged so that a distance between a rotation center of said hub and a swing center of said actuator is at most 40 milli meters ±1 milli meters.
 7. A magnetic disk drive according to claim 1, wherein said hub and said actuator are arranged so that a distance between a rotation center of said hub and a swing center of said actuator is between 40 milli meters and 47.5 milli meters.
 8. A magnetic disk drive according to claim 6 or claim 7, wherein an average access time in locating said magnetic head to said predetermined position on said magnetic disk media, is not greater than 7.5 milli seconds when a torque of said actuator is at least 0.12 Newton.meter per one ampere current.
 9. A magnetic disk drive according to claim 6 or claim 7, wherein an average access time in locating said magnetic head to said predetermined position on said magnetic disk media, is not greater than 7.5 milli seconds when a weight of rotational portion at said actuator is not greater than 36 gram.force.
 10. A magnetic disk drive according to claim 4 further comprising fins arranged around said magnetic disk media.
 11. A magnetic disk drive according to claim 3 or claim 10, wherein said fin is a member having unlevel, washboard or jaggy portion in cross sectional view which is given if said fin is cut by a plane along a rotational axis of said hub.
 12. A magnetic disk drive according to claim 3 or claim 10, wherein said fin is casted en bloc with said housing.
 13. A magnetic disk drive system, comprising: a case mounting and securing a plurality of magnetic disk drive according to claim 2; and a control unit coupling and controling said magnetic disk drives electrically.
 14. A magnetic disk drive system, comprising: a case mounting and securing a plurality of magnetic disk drive according to claim 3; and a control unit coupling and controling said magnetic disk drives electrically.
 15. A magnetic disk drive system according to claim 13 or claim 14, further comprising a fan cooling said plurality of magnetic disk drive or said control unit.
 16. A magnetic disk drive according to claim 4, further comprising fins arranged around said magnetic disk media along a depth direction or a width direction of the magnetic disk drive.
 17. A magnetic disk drive according to claim 16, wherein fins arranged along said depth direction exclusively or along said width direction, have plural rows arranged one another at different positions in the thickness direction of the magnetic disk drive.
 18. A magnetic disk drive according to claim 16, wherein remain fins arranged along said width direction exclusively or along said depth direction, have one row or two rows.
 19. A magnetic disk drive according to claim 3 further comprising a fan making an air flow in a depth direction or a width direction of the magnetic disk drive.
 20. A magnetic disk drive according to claim 10, wherein said housing has a hole to record a servo signal to said magnetic disk media.
 21. A magnetic disk drive system, comprising: a case mounting and securing a plurality of magnetic disk drive according to claim 4, claim 10, or claim 19; and a control unit coupling and controling said magnetic disk drives electrically. 